Electro-optical feedback signal producing apparatus

ABSTRACT

Apparatus and circuitry for positioning a mirror at a desired position includes an electric to rotary motion transducer means connected with the mirror which is controlled by a signal obtained in response to an electrical positioning signal and a feedback signal derived from the actual mirror position. An electro-optical sensing means resonsive to the actual position of the mirror provides the feedback signal. The circuitry is automatically calibrated.

This is a division of application Ser. No. 466,975 filed May 6, 1974 nowU.S. Pat. No. 3,919,545.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention presented herein relates to electro-optical feedbacksignal producing apparatus for use in a control apparatus.

2. Discussion of the Prior Art

Positional accuracy and response speed in placing an object such as ascanning mirror at a desired location has been difficult to attain forany reasonable cost. Difficulty has been encountered in obtaining asignal indicative of the actual position of the object for use as afeedback signal. Open-loop mirror systems which use a galvanometer asthe drive mechanism are available to which a velocity feedback coil isadded to speed up the transient response. Positional accuracy andresponse speed are poor, however. A scanning mirror utilizingcapacitance feedback is available, but is very costly.

SUMMARY OF THE INVENTION

The invention presented herein provides an electro-optical feedbacksignal producing apparatus for us in a control apparatus. The inventionis, for example, usable with circuitry for placing an object such as amirror at a desired position very rapidly and with a high degree ofaccuracy. The apparatus and circuitry includes an electric to motiontransducer means connected with the mirror which is responsive to anelectrical positioning input signal and a feedback signal which isdirectly related to the actual position of the mirror, the feedbacksignal being provided by an electro-optical sensing means responsive tothe actual position of the mirror for providing the feedback signal.

The electric to motion transducer means may be an electric to rotarymotion transducer which includes a pivotally mounted member connectedwith the mirror, a source of magnetic flux positioned adjacent a movableportion of the pivotally mounted member, a coil carried by the pivotallymounted member for coupling with the magnetic flux of the source ofmagnetic flux and a summing amplifier which receives the electricalpositioning signal and the feedback signal to produce an error signalwhich is applied to the coil to position the pivotally mounted memberand the connected mirror.

The electro-optical feedback signal producing apparatus for use in acontrol apparatus includes a light to electric transducer, a lightsource for directing light toward said light to electric transducer anda light shutter positioned to intercept the passage of light to thelight to electric transducer in accordance with the operation of thecontrol apparatus, the output of the light to electric transducerproviding the feedback signal which is directly related to the operationof the control apparatus. The optical sensing means also includes meansto distribute the light flux in a predetermined way at the plane of thelight shutter. The amount of light flux received at the light toelectric transducer is directly controlled by the position of the lightshutter.

Since the output of the light source and the response of the light toelectric transducer are subject to change, the apparatus of thisinvention includes calibration circuitry which provides for automaticcalibration of the electro-optical sensing apparatus. The automaticcalibration circuitry includes an inhibiting circuit which when placedin the calibration mode inhibits the control apparatus from respondingto the electric positioning signal and feedback signal and allows thecontrol apparatus to be positioned for calibration by the application ofa calibrating mode current to the control apparatus. The automaticcalibration portion of the circuitry also includes a light controlcircuit and a control point and memory circuit. The inhibiting circuitwhen placed in the calibration mode allows the control point and memorycircuit to respond to the output of the light to electric transducer toestablish the point of operation of the light control circuit. When theinhibiting circuit is placed in the scanning mode, the memory circuitmaintains the point of operation of the light control circuit which wasestablished during the previous calibration mode.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be understood and its various advantages will becomeapparent from the description to follow given in conjunction with theaccompanying drawing wherein like numerals refer to like elements andwherein:

FIG. 1 is a schematic of apparatus and circuitry for positioning amirror which embodies the invention;

FIG. 2 is a schematic showing of a portion of FIG. 1 together withadditional circuitry for providing automatic calibration of theapparatus and circuitry shown in FIG. 1; and

FIG. 3 is a schematic exemplary showing of circuitry details for thecircuitry portions shown in FIG. 2.

DESCRIPTION

Referring to the drawing, the invention is embodied in the apparatus andcircuitry shown in FIG. 1 which serves to rapidly and accurately placean object such as a mirror 10 at a desired position in response to anelectrical positioning input signal presented at input 22 and a feedbacksignal presented at input 18. The feedback signal is directly related tothe actual position of the mirror. The apparatus and circuitry includesan electrical to motion transducer means 1 illustrated as an electricalto rotary motion transducer, connected with the mirror 10 for placingthe mirror in a position in response to the aforementioned signals andan electro-optical sensing means 2 responsive to the actual position ofthe mirror 10 for providing the feedback signal which varies directlywith the actual position of the mirror 10. The transducer means 1 isconnected to mirror 10, so the position of mirror 10 is determined bythe position of the transducer means 1. The transducer means 1 includesa pivotally mounted member 12, a coil 14 carried on a mandrel secured toone end portion of member 12 and a magnetic flux source 16. In theembodiment of FIG. 1, the mirror 10 is carried directly by member 12 andis positioned above the pivot point 50 for member 12 so mirror 10 ismoved about pivot point 50 as member 12 is moved. The electro-opticalsensing means 2 includes a light source 26, light to current transducer34, and a light shutter operated by the movement of member 12. The lightshutter is shown as including apertured wall 36 and a light vane 40mounted for movement with member 12. The optical sensing means 2 alsoincludes a light control means for receiving light from the light source26 for presenting a predetermined light flux to the plane of the lightshutter which in the structure shown is considered to be the vane 40.The light control means includes concave lens 28 and convex lens 32. Theoptical sensing means 2 is also shown to include second light controlmeans provided by concave lens 30 which serves to collect the converginglight from convex lens 32 passed by the light shutter for presentment tothe transducer 34.

Coil 14 moves relative to the magnetic flux source 16 to establish theposition of mirror 10 and light vane 40. Movement of coil 14 occurs whenthere is current flow in coil 14 with the acceleration determined by theamount of magnetic flux produced by coil 14 which either adds to orsubtracts from the magnetic flux from source 16. The direction andmagnitude of the current flow in coil 14 determines the amount ofmagnetic flux produced by coil 14 and whether it adds to or subtractsfrom the magnetic flux source 16.

Concave lens 28 with convex lens 32 provides a uniform light flux at theplane of vane 40. In this way, a linear relationship is obtained betweenthe vertical position of vane 40 and the amount of light flux receivedat light to current transducer 34. The concave lens 28 serves to diffusethe light from the light source 26 so the lens 28 need not be used if alight source 26 is used which provides a source of diffused light flux.

The position of light vane 40 is in accordance with the position ofmirror 10 and, as shown, serves to vary the amount of light from source26 passed through the aperture 38 in wall 36 to the light to electriccurrent transducer 34 causing the output of transducer 34 to beindicative of the position of mirror 10. The transducer 34 may include aphotodiode 52 and an amplifier 42 connected to the output of thephotodiode. The output of amplifier 42 provides the feedback electricalsignal indicative of the actual position of mirror 10.

The apparatus and circuitry of FIG. 1 also includes a summing amplifiercircuit 20 having input 22 to which the electrical input signal used toestablish a desired position for mirror 10 is applied. Another input 18is provided by amplifier circuit 20 to which the feedback signal fromthe output 41 of amplifier 42 is applied. The output 24 of amplifiercircuit 20 is an error signal which is applied to coil 14. The summingamplifier circuit 20 provides an error signal at output 24 to causecurrent to flow in coil 14 when a difference exists between thepositioning signal at input 22 and the feedback signal at input 18.Accordingly, if no difference in these signals exists, the coil 14 is atthe desired position. If a difference exists, such difference isreflected in the magnitude and polarity of the signal at output 24. Themagnitude of the output signal at 24 is indicative of the absolutedifference between the signals at inputs 18 and 22, while the polarityof the output signal at 24 is indicative of whether the feedback signalat input 18 is greater or less than the positioning signal at input 22.The coil 14 is wound in the direction necessary to cause the magneticflux established by current flow in coil 14 to be such that coil 14moves in accordance with the output or error signal at 24 to cause thefeedback signal from transducer 34 to be equal and opposite to thepositioning signal at input 22 thereby positioning mirror 10 at theposition desired as selected by the mirror positioning input signalprovided at 22.

Considering the apparatus of FIG. 1 in greater detail, the magnetic fluxsource 16 may include a permanent annularly formed magnet 44, which isshown in cross-section in FIG. 1, with a keeper 46 positioned across theend of magnet 44 opposite the end in which the coil 14 is positioned. Apole piece 48 is positioned axially within magnet 44 on keeper 46 andextends toward the coil 14. Thus, if the upper end of magnet 44 is anorth pole, the pole piece 48 will have a south pole induced as itsupper end. The mandrel on which coil 14 is wound is non-magnetic and canbe a paper tube, for example. The mandrel is positioned so it movescoaxially to the pole piece 48. The path for magnetic flux includes thepole piece 48, the air gap from the free end of pole piece 48, magnet 44and keeper 46 back to the other end of pole piece 48. The magnetic fluxcreated by current flow in coil 14 will either add to or subtract frommagnetic flux due to the magnet 44. The direction of movement of coil 14with respect to the pole piece 48 is dependent on the direction ofcurrent flow in coil 14 while the degree of movement is dependent on themagnitude of such current flow. As has been indicated, the magnitude anddirection of the current in coil 14 is determined by the signalpresented at the output 24 of amplifier circuit 20 which in turn isdetermined by the difference between positioning and feedback signals atinputs 22 and 18 respectively, of circuit 20.

Referring to the optical sensing means 2 in greater detail, the lightsource 26, which, for example, may be a miniature incandescent lamp orlight emitting diode, emits light along and around its axis to theconcave lens 28 which serves to distribute this light more evenly overthe solid angle subtended by the convex lens 32 which acts to present aspatially uniform light flux at the aperture 38. The aperture 38 and themovable vane 40 combine to form a variable light stop or shutter whichdetermines how much light flux from lens 32 reaches the photodiode 52via the concave lens 30. The light flux reaching the photodiode 52 isvery closely proportional to the vertical position of the vane 40 whenthe aperture 36 is shaped to a good approximation, like a rectangle.This being the case, the vertical position of vane 40 is very nearlyproportional also to the angular displacement or position of mirror 10since the vertical position of vane 40 is determined by the position ofmember 12 which also determines the angular displacement of mirror 10.The use of the aperture 38 provides a means for correcting forinaccuracies known to occur since the aperture can be shaped to providethe necessary compensation. For example, it can be shaped to compensatefor the absorption of light by the lens or for photodiodenonlinearities. In the case where the mirror is used in a scanningapparatus for scanning a flat surface, the aperture can be shaped withits sides slightly curved to compensate for the optical distortionintroduced by the shortened projections at viewing angles displaced fromthe normal to the surface.

A very nearly linear relationship between angular displacement of mirror10 and light flux reaching photodiode 52 is obtained by having the lightflux at vane 40 as uniform as possible and adjusting the physicalposition of photodiode 52 relative to lenses 30, 32, and 28 such thatphotodiode 52 is in the image plane of the light source 26. As in thecase of concave lens 28, the concave lens 30 may not be required if thephotodiode 52 or similar transducer provides a full response to thelight passed via aperture 38 without having to use a lens to collect thelight and converge it prior to its impinging on the photodiode 52.

The mirror 10 is shown carried on member 12 and is positioned over thepivot point 50 for member 10. It can be appreciated that structure shownfor member 12 with mirror 10 carried directly thereon can be readilymodified. For example, the member 12 can be secured to a shaft mountedfor rotational movement with the mirror carried on the shaft to placethe mirror at a point removed from member 12. It is only necessary thatthe transducer means 1 provide a direct relationship between themovement of coil 14 and the rotational movement of the mirror 10 andmovement of the vane 40.

Another aspect of the invention is concerned with the provision of acalibration means for providing periodic self or automatic calibrationof the apparatus and circuitry of FIG. 1 to correct for variations suchas changes in the light output from lamp 26 or in the response ofphotodiode 52. The circuitry required for providing such automaticcalibration is schematically shown in FIG. 2 wherein portions of thebasic apparatus and circuitry of FIG. 1 are represented together withthe additional circuitry required for providing the automaticcalibration function. The additional circuitry includes a control pointand memory circuit 54, a light control circuit 56 and an inhibit circuit58 and a calibration current circuit 60. The position input signalsource 62 provides the position input signals to input 22 and the enablesignal source 64 provides the control signals for the inhibit circuit58.

The inhibit circuit, dependent on the signal received from the enablesignal source 64a is placed in a calibration mode or in a scanning mode.When the inhibiting circuit 58 is in the calibration mode, amplifier 20is prevented from providing an output at 24 in response to signalsapplied to its two inputs 18 and 22 and when inhibiting circuit 58 is inthe scanning mode, circuit 54 is prevented from responding to the output41 of amplifier 42 of the light to current transducer 34.

When the amplifier circuit 20 is inhibited, current to coil 14 is thenobtained from the calibration current circuit 60. Though this is termeda calibration current circuit, it need not be a precise current. Thecurrent flow is of a direction and magnitude to cause the vane 40 to bepositioned so light can pass via the entire opening presented byaperture 38. With amplifier circuit 20 so inhibited during thecalibration mode, the control point and memory circuit 54 is enabled torespond to the output 41 of amplifier 42 to provide a signal to thelight control 56 in accordance with output 41 for controlling theintensity of light source 26. An initial factory adjustment is made foroperation of lamp 26 at its rated voltage. The signal presented to lampcontrol 56 during the calibration mode of operation will differ fromthat established by the initial factory adjustment of control pointportion of circuit 54 if the output of photodiode 52 is different fromthat presented during the initial factory adjustment of the controlpoint portion. An analog memory is provided in circuit 54 to store thesignal presented to light control 56. When circuit 54 is inhibited by asignal from inhibit circuit 58 for the scanning mode of operation, thememory portion of circuit 54 functions to supply light control 56 withthe control signal entered in the memory portion of circuit 54 duringthe calibration mode of operation.

Exemplary circuits which can be used in the arrangements shown in FIGS.1 and 2 are shown in FIG. 3. A more complete understanding of theoperation of the circuitry of FIG. 2 will be obtained by considering thecircuits of FIG. 3 in detail. That portion of the circuitry of FIG. 3which provides the circuitry functions of the summing amplifier 20 andamplifier 42 of the arrangement shown in FIG. 1 will be consideredfirst.

The summing amplifier circuit 20 includes the operational amplifier 21,the PNP type transistors 23 and 27 plus the NPN type transistors 25 and29. The input signal to input 22 of amplifier circuit 20 is applied tothe inverting input of operational amplifier 21 via a resistor 19. Thefeedback signal from the output 41 of amplifier 42 of the light tocurrent transducer 34 is applied to the same input of amplifier 21 via aresistor 31. The non-inverting input of amplifier 21 is connected toground so amplifier 21 will not present a signal at its output if thesignals applied to inputs 21 and 24 do not produce a current at theinverting input of amplifier 21. When this condition exists there isagreement between the desired and actual position of mirror 10. Anyimbalance between the desired and actual position of mirror 10 willcause a non-zero or error signal output from amplifier 21 to bepresented.

The output from amplifier 21 is coupled to the base of transistors 25and 27 via a resistor 33. The emitters of these transistors areconnected to ground. Transistors 23 and 25 serve to amplify a positivesignal presented at the output of amplifier 21, while transistors 27 and29 serve to amplify a negative output signal presented at the output ofamplifier 21. The collector of transistor 25 and the base of transistor23 are connected via a resistor 35 to a positive voltage source, shownas +22V. The emitter of transistor 23 is also connected to the positivevoltage source. Transistor 23 conducts when transistor 25 is conductingand serves to amplify the conductive action of transistor 25. Thecollector of transistor 23 is connected to the output 24 of circuit 20which is connected to the coil 14 so the current output of transistor 23is effective to alter the position of coil 14. Referring to FIG. 1, thecoil 14 is wound so the current flow from transistor 23 will produce amagnetic flux which adds to the flux provided by magnetic flux source 16causing the coil to move downward as viewed in FIG. 1.

When transistor 27 conducts in response to a negative signal presentedat the output of amplifier 21, transistor 29 conducts to amplify theconducting action of transistor 27 since the base of transistor 29 andthe collector of transistor 27 are connected via a resistor 37 to anegative voltage source, shown as -22V. The emitter of transistor 29 isalso connected to the negative voltage source. The collector oftransistor 29 is connected to the output 24 of circuit 20 which isconnected to coil 14 so current flow in coil 14 due to conduction oftransistor 29 is opposite to that caused by conduction of transistor 23.Accordingly, current flow in coil 14 due to conduction of transistor 29produces magnetic flux which opposes the flux from magnetic flux source16 thereby causing coil 14 to move upwardly as viewed in FIG. 1.

To complete circuit 20, a feedback resistor 49 is connected between theoutput 24 of circuit 20 to the inverting input of amplifier 21. Inaddition, a resistor 53 and a series connected capacitor 55 areconnected in parallel with resistor 19. A resistor 57 and capacitor 59are connected in a similar fashion across resistor 31. Resistors 53, 57and capacitors 55, 59 provide feedforward compensation so as to properlydamp the system.

FIG. 3 shows the light to current transducer 34 in greater detail. Asshown, photodiode 52 has its anode connected to a negative voltagesource, shown as -15V, while its cathode is connected to the negativeinput of amplifier 42 which has its positive input connected to ground.Negative input of amplifier 42 is also connected to a positive voltagesource shown as +15V through variable resistor 45. A feedback resistor51 is connected between the output of amplifier 42 and its negativeinput.

The circuitry described to this point with respect to FIG. 3 providescircuitry suitable for use in the arrangement shown in FIG. 1. Theremaining circuitry of FIG. 3 is that which is needed to carry out theself or automatic calibration operation described in connection withFIG. 2. The control point and memory circuit 54 and lamp control circuit56 will be described before considering the details of the inhibitcircuit 58.

The control point circuit portion of circuit 54 includes an operationalamplifier 63 and series connected potentiometer 65 and resistor 67connected between ground and a positive voltage source shown as +15V.The adjustable contact of potentiometer 65 is connected to the negativeinput of the amplifier 63. The positive input for amplifier 63 isconnected to the output 41 of amplifier 42 at which the feedback signalfrom the optical means 2 is presented. The potentiometer 65 is adjustedwhen the apparatus and circuitry of FIG. 2 is installed for use inequipment and in that sense is a factory type of adjustment.

The memory portion of circuit 54 includes a field effect transistor 75,operational amplifier 77 and capacitor 66. A resistor 69 connected inseries with parallel connected and oppositely poled diodes 71 and 73serves to couple the output of amplifier 63 to the gate of the fieldeffect transistor 75 which has its drain electrode connected to thenegative input of an operational amplifier 77. The drain electrode oftransistor 75 is connected also to a negative voltage source, shown as-15V via a resistor 79. The source electrode of field-effect transistor75 is connected to a positive voltage source, shown as +15V. Thepositive input of amplifier 77 is connected to a positive voltageprovided at the connection common to series connected resistors 81 and83 which are connected between ground and a positive voltage source,shown as +15V. The capacitor 66 is connected between the output ofamplifier 77 and the gate of transistor 75 to complete the memoryportion of circuit 54. The field-effect transistor 75 and amplifier 77with capacitor 66 provide an integrating circuit having an extremelylong time constant. The memory circuit portion of circuit 54 causes theoutput of amplifier 77 to continue to operate at the level it wasoperating upon termination of any input from amplifier 63 in response tothe placement of the inhibit circuit 58 in the scanning mode ofoperation.

The output of amplifier 77 is connected to the base of an NPN typetransistor 85 via a resistor 87. The transistor 85 is a part of the lampcontrol circuit 56 which serves to control the current flow through thelamp 26 in accordance with the signal presented to the base oftransistor 85. A positive voltage source, shown as 15V, is connected tothe collector of transistor 85 and is also connected to the base oftransistor 85 via a resistor 89 and to one side of lamp 26 via aresistor 91. The emitter of transistor 85 is connected to the same sideof lamp 26 via a resistor 93. The other side of lamp 26 is connected toground.

The control point portion of the circuit 54 comes into play only whenthe circuitry is initially calibrated and during those times when thecircuitry is conditioned for the automatic calibration mode of operationas determined by the inhibit circuit 58. Initial and automaticcalibration is done with the vane 40 positioned so it does not interferewith the passage of light via the aperture 38. During the initialcalibration, the light source 26 is energized by a voltage source (notshown) of selected level, for example, the rated lamp voltage. Thepotentiometer 65 is then adjusted so the input of the negative input foramplifier 63 is egual to the input to the positive input terminal.Should the output from the photodiode 52 subsequently vary because of achange in the response of the photodiode itself or because of a changein the intensity of the light received from lamp 26, which can be due toany number of factors, the two inputs to amplifier 63 will be differentcausing a signal to be presented at the output of amplifier 63. Duringthe automatic calibration mode, the inhibit circuit 58 will permit suchoutput to be applied to the field-effect transistor 75 causing a changein the output of amplifier 77 to change the conduction of transistor 85and therefore the current through lamp 26 whereby the light intensity isvaried. The light from lamp 26 is optically fed back by the opticalsensing means 2 to th photodiode 52 so the input signals to amplifier 63are again equal. When the calibration mode is terminated by action ofthe inhibit circuit 58 placing the circuitry in the scanning mode, thevoltage on capacitor 66 causes the amplifier 77 to have the same outputas it had when in the calibration mode, so lamp 26 continues to operateat the current level established by the calibration mode until thecalibration mode is repeated by the inhibit circuit 58.

It has been indicated that during the calibration mode of operation, thevane 40 is positioned so it does not interfere with the passage of lightthrough the aperture 36. This is accomplished when the operation ofsumming amplifier 20 is inhibited by the inhibit circuit 58 operating toclamp the bases of transistors 25 and 27 to ground. With transistors 25and 27 off, transistors 23 and 29 will not conduct so coil 14, whichcontrols the position of vane 40, will be conducting in accordance withthe current from calibration current circuit 60 which as can be seen inFIG. 3 is determined by the positive voltage source (+22V) and a singleresistor. The current drawn by coil is then of the proper magnitude anddirection to cause vane 40 to be positioned so as to not interfere withthe passage of light through the aperture 38.

The inhibiting circuit 58 includes two operational amplifiers 68 and 70.Amplifier 68 has its positive input connected to an enable signal source64 while amplifier 70 has its negative input connected to such source.The signal from source 64 is a high signal, say 5 volts, when normal orscanning mode of operation of the mirror 10 is desired and is a lowsignal, say 0 volts, when the calibration mode is desired. The negativeand positive inputs of amplifiers 68 and 70, respectively, are connectedto receive a positive biasing voltage. Such positive voltage is obtainedat the connection common to the series connected resistors 72 and 74connected between a positive voltage source, shown as 15 volts, andground, respectively. Each of the amplifiers 68 and 70 are resistivelycoupled to similar diode circuits. The output of amplifier 68 isconnected via resistor 76 to the anodes of diodes 80 and 82 and to thecathodes of diodes 78 and 84. The anode of diode 78 and the cathode ofdiode 80 are connected to ground so diodes 78 and 80 are connected inparallel, but oppositely poled. A resistor and diodes are similarlyconnected to the output of amplifier 70, such elements being identifiedwith like reference numerals to which a prime indication has been added.The cathode of diode 82 and the anode of diode 84' are each connected tocircuitry 54 and specifically to the connection common to resistor 69and diodes 71, 73. The cathode of diode 82' and the anode of diode 84are connected to the base electrodes of transistors 25 and 27 ofamplifier 20.

With the inhibiting circuit 58 described, a high or scanning mode inputsignal from the enable signal source 64 allows up to a +1.4 volt swingat the bases of transistors 25 and 27, which is sufficient for normaloperation of mirror 10, while diodes 82 and 84' serve to prevent theflow of any current through diodes 71 and 73. At this time, slightsignal variations will be presented to diodes 71 and 73, but these arenot large enough to overcome the 0.7 volt required for conduction ofdiodes 71 and 73 so no signal from amplifiers 63 passes to thefield-effect transistor 75. Accordingly, with the inhibiting circuit 58receiving a high or scanning mode input signal from source 64, thesumming amplifier circuit 20 will operate to permit mirror 10 to bepositioned in accordance with signals received from input signal source62, while operation of circuit 54 in accordance with the output fromamplifier 63 is inhibited.

When a low or calibration mode signal is presented to the inhibitingcircuit 58 from the enable signal source 58, the base electrodes oftransistors 25 and 27 are clamped to ground to disable operation ofamplifier 20, while current is allowed to pass through diodes 71 and 73to transistor 75 permitting the current via lamp 26 to be varied asrequired to equalize the input signals to amplifier 63 and therebyrestore the calibration of the optical sensing means 2. As has beenmentioned, the output of amplifier 77 required to provide calibration iscontinued after the calibration mode is terminated since capacitor 66,field effect transistor 75 and amplifier 77 function as an analogmemory.

The apparatus and circuitry described provide an excellent means for thecontrol of a mirror for use in any type of instrument requiring veryaccurate and rapid control of a scanning or operating light beam. Thebeam can be directed by the use of two mirrors, one mirror for movementor direction of the beam in the x direction and the other mirror fordirection of the beam in the y direction.

The apparatus and circuitry described here can also be applied tomovement of other objects than the mirror described above. It can beused equally well for precise movement of a lens, diffraction grating,prism, pointer, or other device. In addition, the electro-opticalsensing means described can be used to provide a feedback signal inother control apparatus wherein the shutter position is controlled inresponse to operation of the apparatus.

In the light of the above teachings, alternative arrangements andtechniques embodying the invention will be suggested to those skilled inthe art. The scope of protection afforded the invention is not intendedto be limited to the specific embodiments disclosed, but is to bedetermined only in accordance with the appended claims.

What is claimed is:
 1. Electro-optical feedback signal producingapparatus for use in a control apparatus including: a light means forproviding a uniform light flux distribution, a light to electrictransducer having an output at which the feedback signal is provided, alight shutter positioned with respect to said light means for receivingsaid uniform light flux distribution and operatively responsive to theoperation of the control apparatus for controlling the passage of lightvia said shutter in accordance with the operation of the controlapparatus and light control means positioned with respect to said lightmeans and said light shutter for converging at said light to electrictransducer the light flux presented at said light shutter.
 2. Apparatusin accordance with claim 1 wherein said light control means includes aconvex lens.
 3. Apparatus in accordance with claim 1 wherein saidcontrol means includes a convex lens and said light means includes alight source and a concave lens with said convex lens positioned betweensaid light shutter and said concave lens.
 4. Apparatus in accordancewith claim 1 wherein said light shutter includes an aperture and a vanemovable in accordance with the position of the object and said apertureis shaped to provide a desired relationship between the position of saidvane and the output of said light to electric transducer.
 5. Apparatusin accordance with claim 1 wherein the apparatus further includes lightcontrol means positioned between said light shutter and said light toelectric transducer for collecting the light passed by said shutter andpresenting it to said transducer.
 6. Apparatus in accordance with claim2 wherein said light means includes a light source and said light toelectric transducer is positioned at the image plane of said lightsource.
 7. Apparatus in accordance with claim 5 wherein said lightcontrol means positioned between said light shutter and said transducerincludes a concave lens.
 8. Apparatus in accordance with claim 1 whereinsaid light control means includes a convex lens and the apparatusfurther includes light control means positioned between said lightshutter and said light to electric transducer for collecting the lightpassed by said aperture and presenting it to said transducer. 9.Apparatus in accordance with claim 8 wherein said light means includes alight source and said light to electric transducer is positioned at theimage plane of said light source.
 10. Apparatus in accordance with claim8 wherein said light control means positioned between said light shutterand said transducer includes a concave lens.
 11. Apparatus in accordancewith claim 1 wherein said light shutter has a calibration position andsaid apparatus includes calibration circuitry including a light controlcircuit connected for controlling said light means and a control pointand memory circuit connected for controlling said light control circuit,said control point and memory circuit connected to receive said feedbacksignal for establishing a control signal for controlling said lightcontrol circuit, said control point and memory circuit connected forresponding to said feedback signal only when said light shutter is inits calibration position and said control signal continuing after thecalibration position of said light shutter is terminated and until suchtime as said light shutter is again placed in the calibration position.